Band Selection
Band selection enables client radios that are capable of dual-band (2.4 and 5-GHz) operations to move to a less congested 5-GHz access point. The 2.4-GHz band is often congested. Clients on this band typically experience interference from Bluetooth devices, microwave ovens, and cordless phones as well as co-channel interference from other access points because of the 802.11b/g limit of 3 nonoverlapping channels. To prevent these sources of interference and improve overall network performance, configure band selection on the controller.
Band selection works by regulating probe responses to clients and it can be enabled on a per-WLAN basis. It makes 5-GHz channels more attractive to clients by delaying probe responses to clients on 2.4-GHz channels. In an access point, the band select table can be viewed by running the show dot11 band-select command. It can also be viewed by running the show cont d0/d1 | begin Lrucommand.
![]() Note |
The WMM default configuration is not shown in the show running-config command output. |
Band Selection Algorithm
The band selection algorithm affects clients that use 2.4-GHz band. Initially, when a client sends a probe request to an access point, the corresponding client probe’s Active and Count values (as seen from the band select table) become 1. The algorithm functions based on the following scenarios:
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Scenario1: Client RSSI (as seen from the show cont d0/d1 | begin RSSI command output) is greater than both Mid RSSI and Acceptable Client RSSI.
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Dual-band clients: No 2.4-GHz probe responses are seen at any time; 5-GHz probe responses are seen for all 5-GHz probe requests.
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Single-band (2.4-GHz) clients: 2.4-GHz probe responses are seen only after the probe suppression cycle.
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After the client’s probe count reaches the configured probe cycle count, the algorithm waits for the Age Out Suppression time and then marks the client probe’s Active value as 0. Then, the algorithm is restarted.
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Scenario2: Client RSSI (as seen from show cont d0/d1 | begin RSSI ) lies between Mid-RSSI and Acceptable Client RSSI.
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All 2.4-GHz and 5-GHz probe requests are responded to without any restrictions.
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This scenario is similar to the band select disabled.
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![]() Note |
The client RSSI value (as seen in the sh cont d0 | begin RSSI command output) is the average of the client packets received, and the Mid RSSI feature is the instantaneous RSSI value of the probe packets. As a result, the client RSSI is seen as weaker than the configured Mid RSSI value (7-dB delta). The 802.11b probes from the client are suppressed to push the client to associate with the 802.11a band. |
Restrictions for Band Selection
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Band selection-enabled WLANs do not support time-sensitive applications such as voice and video because of roaming delays.
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Band selection can be used only with Cisco Aironet 1530, 1570,1700, 1800, 2700, 2800, 3700, 3800 Series APs.
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Band selection operates only on access points that are connected to a controller. A FlexConnect access point without a controller connection does not perform band selection after a reboot.
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The band-selection algorithm directs dual-band clients only from the 2.4-GHz radio to the 5-GHz radio of the same access point, and it only runs on an access point when both the 2.4-GHz and 5-GHz radios are up and running.
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You can enable both band selection and aggressive load balancing on the controller. They run independently and do not impact one another.
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It is not possible to enable or disable band selection and client load balancing globally through the controller GUI or CLI. You can, however, enable or disable band selection and client load balancing for a particular WLAN. Band selection and client load balancing are enabled globally by default.
Configuring Band Selection (GUI)
Procedure
Step 1 |
Choose Wireless > Advanced > Band Select to open the Band Select page. |
Step 2 |
In the Probe Cycle Count text box, enter a value between 1 and 10. This cycle count sets the number of 2.4 GHz probe suppression cycles. The cycle count sets the number of suppression cycles for a new client. The default cycle count is 2. |
Step 3 |
In the Scan Cycle Period Threshold (milliseconds) text box, enter a value between 1 and 1000 milliseconds for the scan cycle period threshold. This setting determines the time threshold during which new probe requests from a client come from a new scanning cycle (i.e. only if the time difference between the successive probe requests is greater than this configured value, then the count value in the band select table increases). The default cycle threshold is 200 milliseconds. |
Step 4 |
In the Age Out Suppression (seconds) text box, enter a value between 10 and 200 seconds. Age-out suppression sets the expiration time for pruning previously known 802.11b/g/n clients. The default value is 20 seconds. After this time elapses, clients become new and are subject to probe response suppression. |
Step 5 |
In the Age Out Dual Band (seconds) text box, enter a value between 10 and 300 seconds. The age-out period sets the expiration time for pruning previously known dual-band clients. The default value is 60 seconds. After this time elapses, clients become new and are subject to probe response suppression. |
Step 6 |
In the Acceptable Client RSSI (dBm) text box, enter a value between –20 and –90 dBm. This parameter sets the minimum RSSI for a client to respond to a probe. The default value is –80 dBm. |
Step 7 |
In the Acceptable Client Mid RSSI (dBm) text box, enter a value between –20 and –90 dBm. This parameter sets the mid-RSSI, whose value can be used for toggling 2.4 GHz probe suppression based on the RSSI value. The default value is –60 dBm. |
Step 8 |
Click Apply. |
Step 9 |
Click Save Configuration. |
Step 10 |
To enable or disable band selection on specific WLANs, choose WLANs > WLAN ID. The WLANs > Edit page appears. |
Step 11 |
Click the Advanced tab. |
Step 12 |
In the Load Balancing and Band Select text area, if you want to enable band selection, select the Client Band Select check box. If you want to disable band selection, leave the check box unselected. The default value is disabled. |
Step 13 |
Click Save Configuration. |
Configuring Band Selection (CLI)
Procedure
Step 1 |
Set the probe cycle count for band select by entering this command: config band-select cycle-count cycle_count You can enter a value between 1 and 10 for the cycle_count parameter. |
Step 2 |
Set the time threshold for a new scanning cycle period by entering this command: config band-select cycle-threshold milliseconds You can enter a value for threshold between 1 and 1000 for the milliseconds parameter. |
Step 3 |
Set the suppression expire to the band select by entering this command: config band-select expire suppression seconds You can enter a value for suppression between 10 to 200 for the seconds parameter. |
Step 4 |
Set the dual band expire by entering this command: config band-select expire dual-band seconds You can enter a value for dual band between 10 and 300 for the seconds parameter. |
Step 5 |
Set the client RSSI threshold by entering this command: config band-select client-rssi client_rssi You can enter a value for minimum dBm of a client RSSI to respond to a probe between -20 and -90 for the client_rssi parameter. |
Step 6 |
Set the client mid RSSI threshold by entering this command: config band-select client-mid-rssi client_mid_rssi You can enter a value for mid RSSI between -20 and -90 for the client_mid_rssi parameter. |
Step 7 |
Enter the save config command to save your changes. |
Step 8 |
Enable or disable band selection on specific WLANs by entering this command: config wlan band-select allow {enable | disable} wlan_ID You can enter a value between 1 and 512 for wlan_ID parameter. |
Step 9 |
Verify your settings by entering this command: show band-select Information similar to the following appears:
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Step 10 |
Enter the save config command to save your changes. |